Reducing Environmental Contamination from Feedlot Manure in the South Platte River Basin through Agronomic, Economic, and Social Analysis and Education

Final Report for SW96-007

Project Type: Research and Education
Funds awarded in 1996: $206,000.00
Projected End Date: 12/31/1999
Matching Non-Federal Funds: $73,191.00
Region: Western
State: Colorado
Principal Investigator:
Dr. Jessica Davis
Colorado State University
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Project Information


Impacts of manure application rates on crop yields, nitrate levels, weed and insect populations, and microbial biomass were examined in a two year field test on two farmers' fields. One field had a clay soil with no manure application history, and the other field had a sandy soil with a long history of manure application. Over application of manure did not improve yield and can harm soil and water quality. Manure application increased soil nitrate within and below the rootzone in early summer. Manure application increased microbial biomass nitrogen, suppressed proso millet germination, but had no effect on corn rootworm. A study with ten manure haulers showed that most manure haulers do achieve their application rate goals, but about two thirds of them had poor spreader uniformity. A survey of 270 farmers showed that producers value manure at $3.85 per ton due to its positive impact on soil properties. We held eight workshops for livestock producers and helped 53 producers develop manure management plans for their farms.

Project Objectives:

Research Objectives

1. Determine optimum feedlot manure application rates and accompanying N fertilizer needs for silage corn and to use the pre sidedress soil nitrate test and the chlorophyll meter as a guide for in season N recommendations in manured fields.

2. Determine crop water use and nitrate loss below the root zone as a function of manure application rate and timing.

3. To evaluate the effect of manure rates on soil quality and microbial populations and on pest populations (weeds, diseases, insects) and management recommendations.

4. Compute the costs and returns to alternative management schemes, determine economic returns and constraints for hauling, and understand the decision making processes and relationships of persons and organizations in the chain from feedlot stocks of manure to potential users of manure as a fertilizer.

Education Objectives

1. Change the perception of manure as a waste to its being viewed as a valuable resource and to increase the use of manure credits so that applications will be made at agronomic rates and environmental problems minimized.

2. Encourage feedlot operators to conduct manure testing and to give the nutrient analysis of each load to the recipient.

3. Train manure haulers/spreaders in calibration of their equipment and proper application techniques.

4. Teach consultants, fertilizer dealers, and producers to base fertilizer recommendations on soil testing, manure analysis and calibration, the pre sidedress soil nitrate test, and chlorophyll meter measurements.


Research results and discussion:

Research Objective 1

Field studies were established in Weld County in 1997 to evaluate beef feedlot manure impacts in irrigated cropping systems. One field had a clay soil (Nunn series) with no manure applications in the last eight years (except for one application in the fall of 1995). The other field had a sandy loam soil (Vona series) with a long history (>50 years) of beef manure applications. In 1998, the sandy site was relocated to another sandy field (Valent loamy sand) with a long history of turkey and beef manure applications. All three fields were irrigated through center pivot systems. Each field was laid out with four replications, four manure treatments (0, 10, 20, and 30 tons manure per acre), and two sidedress nitrogen treatments (0 and 50 lbs/acre) in splitplot designs, with manure treatments as the main treatments and sidedress nitrogen as the split plots.

Manure came from on farm or nearby beef cattle feedlots. The manure treatments were applied in the early spring and incorporated immediately after application. There were no effects from sidedress nitrogen applications at either field, nor any effect from manure treatments on yield at the sandy site. There was a significant impact of manure rates on corn yield at the clayey site, however. The higher manure application rates improved stand in the clayey soil, and, subsequently, increased yield.

Three of the four site years evaluated had no significant yield differences due to manure application rates. This is probably due to the long term manure application histories on the sandy sites and the long term fertilization of the clayey site. Overapplication of manure (30 ton/acre rate) did not improve yield at any location and can harm soil and water quality.

Research Objective 2

Nitrate movement was assessed by collecting soil samples from each of the fields at three times: pre season (before manure application), mid season, and crop harvest. Six cores were taken down to a depth of six feet in each plot at each sampling time. The initial nitrate levels prior to manure application were about 60% higher in the clay loam soil than in the sandy loam soil, in spite of the lack of manuring history. The 10 and 30 tonlacre manure application rates both showed a trend of elevated nitrate levels both within (0-4 ft) and below the rootzone (4-6 ft) in both fields. In the pre season to mid season period, all manured plots had increased soil nitrate levels, and the 30 ton/acre rate had greater increases (39%) as compared to the 10 ton/acre manure application rate (22%). Soil nitrate increased below the rootzone in all treatments from pre season to mid season, even those without current manure application. This was particularly true in the sandy loam soil, probably due to the previous long term manure application. By mid season (especially in the sandy loam soil), decreases in soil nitrate in the upper profile were accompanied by elevated soil nitrate in the subsoil due to the combined effects of plant uptake and leaching.

From mid season to harvest time, soil nitrate level decreased below the rootzone in all plots, but the decline was much greater in the sandy soil (18%) than in the clayey soil (3%). Within the rootzone during the late summer, soil nitrate levels increased in the clay soil (9%) and decreased in the sandy soil (30%). The combined effects of crop uptake and leaching resulted in these reductions in soil nitrate. It is difficult to separate these two effects. However, within the rootzone of the clay soil, soil nitrate increased even in late summer. A portion of the nitrate buildup in the clay loam soil can be attributed to high nitrate concentrations (10 mg N03 N/L) in the irrigation water (alluvial groundwater).

In summary, soil nitrate concentration below the rootzone increased in early summer and decreased in late summer. The spring manure application resulted in excess soil nitrate when the corn was still small, its need for nitrogen was not great, and the root system was not fully developed. In addition, early season nitrate accumulation may be a result of manure and fertilizer buildup from previous years.

Research Objective 3


The effects of manure application on weed seedling population dynamics are two fold. First of all, manure applications may increase the density and diversity of the weed seeds in the weed seedbank through the addition of seeds contained in the manure. Secondly, nutrients in manure may affect the weed population by stimulating weed seedling growth. The effects of manure rates on weed seedling population dynamics were evaluated by counting weed seedling densities. Weed seedling sampling was conducted prior to a post emergence herbicide application, in early June of each year.

The density and type of weed seedling species between experimental sites varied. The sandy site tested in 1997 was the most severely weed infested field of those studied. The clayey site was moderately infested, and we observed no weed seedlings in the sandy site used in 1998. In the severely infested field, there were 13 weed seedling species that were observed (pigweed, lambsquarters, spurred anoda, barnyard grass, common mallow, velvetleaf, Canada thistle, kochia, dandelion, tooth spurge, smart weed, bindweed, and nightshade).

Eight weed species were detected in 1997 and 1998 in the moderately infested field (pigweed, velvetleaf, common sunflower, cocklebur, buffalobur in 1997 only, kochia in 1998 only, common mallow, bindweed, and proso millet). Proso millet seedling density was greater than the other seven broadleaf seedling populations. The predominant broadleaf species was cocklebur. Across both sites, broadleaf species occurred in higher densities in the severely infested field; however, the grass population (specifically, proso millet) was greater in the moderately infested field.

The highest density of proso millet occurred in the treatment where no manure was applied. No significant difference was detected at a p value of 0.05 within or among treatments for any weed seedling species in 1997 or 1998, except for proso millet in the moderately infested field. Across both years the mean density of proso millet was greater when no manure treatment was applied and decreased as rates of manure increased. In 1997, proso millet mean density from plots treated with 0 or 10 T/A of manure were significantly greater than densities from plots treated with 20 or 30 T/A of manure. When the experiment was conducted again in 1998, proso millet mean densities from plots treated with 0 T/A of manure were significantly greater than mean densities from plots treated with either 20 or 30 T/A of manure. It is speculated that some factor related to the manure may have inhibited proso millet seed germination.


The manure test plots were evaluated for insect damage, as well as weed populations. Previous studies in more humid environments indicated that manuring increased corn rootworm populations and caused subsequent reductions in yield. We evaluated the relationship between manure application rates and rootworm damage to see if it held true in our semi arid environment.

Insect damage to corn plants was evaluated at harvest on both fields. Corn rootworm damage was assessed by digging up plants and inspecting roots. Corn rootworm ratings were based on the Iowa 1-6 system, where 1 = no damage to roots and 6 complete removal of root system. One plant per plot was evaluated for rootworm damage. Rootworm damage was very even across all treatments on both fields. Ratings indicated very little effect on yield due to damage by rootworms. There was no significant impact on rootworm damage due to manure application rates.


Manure applications to soil may have substantial effects on soil organisms and their activities. These effects may be beneficial or detrimental to the sustainability of crop production. The objectives of the soil biology studies were to analyze the impact of manure application rate on biological activity, microbial biomass, and earthworms in the SARE plots.

The substrate induced respiration method was used to estimate active biomass carbon, the fumigation incubation method was used to measure total biomass carbon, and the fumigation extraction method was used to measure microbial biomass nitrogen. Both sites (two replicates) were sampled in the fall of 1997. In 1998, both sites were sampled twice (in June and September). Each sample consisted of ten soil composites taken to a depth of 15 cm.

Both active and total biomass carbon tended to be greater in the clayey sites than in the sandy sites. However, manure application increased microbial biomass nitrogen in both the sandy and clayey soils in 1998. Manure also increased total biomass carbon in the sandy soil in 1997. Sidedressed nitrogen fertilizer also influenced microbial activity. Sidedressing significantly increased the biomass nitrogen in all three fields. Therefore, both manure and nitrogen fertilizer stimulated microbes and increased microbial biomass nitrogen.

Soil samples were collected for earthworm counts from each site in fall 1997 and in both June and September of 1998. Earthworms (adults and cocoons) were counted and identified to the species level. Earthworm counts were too low to analyze statistically. Factors such as tillage, rootworm pesticide applications, or salts may have a strong dampening effect on earthworm populations at these sites.

Research Objective 4

We conducted a mailed questionnaire survey of crop producers in Weld County, inquiring as to their views about and uses of manure. During November and December 1998, questionnaires were mailed to all persons (approximately 1000) identified as owners of cropland in the feedlot intensive area of Weld County, near Greeley. About 270 persons responded to the survey, which solicited several kinds of information, including: 1) General descriptive questions about the operator's farm/ranch; 2) Two parallel series of questions about a) a typical field (if any) to which the operator had applied manure during the past season, and b) a typical field to which the operator had not applied manure; 3) Questions concerning the economic value, positive or negative, that the operator placed on manure as a soil amendment; and 4) A series of questions concerning perceptions of the benefits and problems associated with applying manure to crops.

Respondents to the survey represented producers typical of Weld County. Average total acreage of operation was about 500 acres, with most oriented in one way or another to animal production. For the majority of producers, corn (shell or silage) constituted the largest single crop, typically followed by other feed crops, such as alfalfa or hay. Forty three percent of all operators were engaged in some kind of animal production, with cattle being the most common species.

About half (53%) of persons surveyed reported having applied manure to at least one of their fields during the past year, with nearly half of those (44%) saying that they obtained most of what they used from their own livestock. On fields to which manure was applied, average usage was 19 tons per acre. On those fields operators saw as suitable for manure application, 66% of those who had their own source of manure said they applied manure at least every other year. Among operators who relied on off farm manure sources, 55% of those who applied manure this year indicated that their typical practice involved application of manure at least every other year.

Over 80% of producers saw manure as having positive economic value. On average, these people indicated that manure was worth $4.80 per ton to them. Those who indicated that manure had negative value to them said, on average, that they would have to be paid $2.50 per ton to accept manure spread on their fields. Averaging negative and positive values across all producers, the average per ton value of manure was (+) $3.85.

Producers were asked to respond to a series of questions concerning the importance of potential benefits of manure use, such as "Inexpensive Fertilizer" and potential problems, such as "Salt Damage to Plants." Responses to these questions suggest that most producers view manure positively. On a scale of 5 (important) to 1 (Not Important), the average score for Benefits was 3.9, as opposed to only 2.7 for the Problems. Even the least important Benefit ("Prevents Wind Erosion") ranked nearly as high as the most important Problem. Benefits seen as most important included "Improves Soil Properties" and "Source of Organic Matter," while the most important problem was "Causes More Weeds," followed by "Soil Compaction." These attitudes toward manure use did show up in producers actual behavior, with high scores on importance of Benefits and low scores on importance of Problems being associated with substantially increased chances of having used manure on at least one field last year.

While it seems natural to suspect that producers' perceptions of the economic and agronomic value of manure might affect propensity to use it, we also investigated how field specific factors influenced whether a particular field was chosen for manure application. Neither the kind of crop grown, nor whether a field was leased or owned, nor the current status of weed problems in a field, nor the past yield history of a field affected the chances of it being manured. Distance of a field from a manure source, and size of the field had the most effect on the manure use decision, with greater distance and larger field size showing strong negative associations with a field having been manured.

Research conclusions:

We expect that the outcomes of this project are better optimization of manure applications to plant needs, which should reduce the chances of nitrate leaching into groundwater supplies. Improving manure handling and increasing the perception of it as a high quality plant food may increase the use of manure, in terms of both numbers of farmers and distance utilized from manure sources. Our biggest impacts are development of CNMPs by 53 livestock producers in the South Platte River Basin, improvements in manure spreader calibration and spread uniformity, the publication of a series of eight factsheets, education of nearly 800 farmers about manure issues and the environment, and education of 17 university scientists and graduate students about how producers make manure management decisions and what constraints they face.

Participation Summary

Research Outcomes

No research outcomes

Education and Outreach

Participation Summary:

Education and outreach methods and analyses:
Dissemination of Findings

Education Objective 1

We wrote an entire issue of our departmental extension newsletter, From the Ground Up Agronomy News, with a focus on this SARE project. This newsletter was sent to the members of the Colorado Livestock Association, Certified Crop Advisors, and extension agents throughout Colorado. It is enclosed for your information and is also available on the web at:

Presentations on composting as a means of increasing manure value were made to four workshops: Healthy Plains Initiative, Home on the Front Range, Alamosa County Commissioners, and Colorado Horse Council. Visits have also been made to horse, sheep, and dairy producers who asked for information about composting.

We presented information gained from the project at a number of meetings. These include:

• Regulations and Challenges for Feedlot Manure in Colorado. Lethbridge Res. Ctr., Alberta, Canada;
• Comparison of Manure Spreader Calibration Methods and Operator Goals. National meetings of the American Society of Agronomy, Baltimore;
• Manure Spreader Uniformity and Calibration Methods. Animal Production Systems and the Environment, Des Moines;
• Nitrate Leaching under Variable Rates of Manure Application. Animal Production Systems and the Environment, Des Moines;
• SocioEconomic Issues Affecting Groundwater Pollution Near Cattle Feedlots. Animal Production Systems and the Environment, Des Moines;
• Variability of Manure Nutrient Content and Impact on Manure Sampling Protocol. Animal Production Systems and the Environment, Des Moines;
• Regulations and Challenges for Feedlot Manure in Colorado. National Animal Science Conference, Denver, CO;
• Variability of Manure Nutrient Content and Impact on Manure Sampling Protocol. Great Plains Soil Fertility Conference, Denver;
• Nitrogen Mineralized from Manure Amended Soils. Great Plains Soil Fertility Conference, Denver; Soil Nitrate Movement under Cropland Fertilized with Feedlot Manure. Great Plains Soil Fertility Conference, Denver.

Education Objective 2

Manure and compost samples were collected from eastern Colorado, analyzed, and compared to the book values commonly used to predict nutrient content of manures. The Colorado samples differed significantly from the book values, which had come from Midwest sources a number of years ago. Methods of sampling manure were demonstrated at two "Manure Tour" workshops. A workshop with 30 managers and technicians from 20 western soil test labs covered methodology of manure analysis and how to make nitrogen fertilizer recommendations from them.

Eight fact sheets were developed to provide information on manure analysis and recommendations to growers. All of these factsheets are available on the web at:

• Selecting an analytical laboratory (0.520)
• Cattle manure application rates (0.560)
• Manure spreader calibration (0.561)
• Horse manure: a renewable resource (1.219)
• Feedlot manure management (1.220)
• Liquid manure management (1.221)
• Liquid manure application to cropland (1.222)
• Liquid manure application methods (1.223)

Education Objective 3

Five "Manure Tour" workshops were held in 1996 and 1997 in Weld, Yuma, Montrose, Otero, and Prowers counties. These workshops covered a variety of topics concerning manure management issues, including calibration of manure spreaders.

CSU's nutrient management calculations result in a very precise recommended manure application rate. However, due to the variable nature of manure and the variability of application by solid manure spreaders, farmers usually can not apply manure as precisely as we can calculate a rate. The variability in manure spreading is due in part to equipment problems such as failure of beater bars to break up clods, variable rates of feed aprons, and sloughing of manure from the spreader sides during application. Very few manure haulers calibrate their manure spreaders; most feel that they can estimate the application rate based on experience and can adjust the spreader according to the wetness of the manure.

We worked with ten manure haulers to test spreader uniformity and calibration techniques. Two calibration methods were evaluated. The Tarp Method in which the spreader operator drives over three tarps, the manure on the tarps is weighed, and an application rate is calculated by dividing by the area of the tarps. The Swath Width and Distance Method requires truck scales so that the manure spreader can be weighed full and empty. The manure is spread, and the swath width and distance traveled is measured; then the rate can be calculated by dividing the weight by the area.

The Swath Width and Distance Method resulted in significantly higher measured application rates than the Tarp Method. The variability across tarps averaged 30%; this amount of variability is innate to manure spreading. However, the application rate goals, stated by the manure haulers before spreading, were not significantly different from either spreader calibration method. Manure haulers applying manure for other producers are paid to apply a defined application rate, and most are achieving their application rate goals. We did not evaluate manure application rates spread by farmers on their own land.

Seven out of ten manure spreaders had spread patterns which were off center. Some of the trucks did not seem to be loaded evenly, but trucks were loaded according to common procedure; therefore, the unevenness of the spreading could be partially attributed to asymmetrical loading and partially attributed to the need for adjustment and improvement of manure spreaders. Swath widths ranged from 7 1/2 ft to 16 ft. Therefore, the haulers must adjust their overlap patterns depending on the swath width, in order to achieve a more uniform spread.

Education Objective 4

We held a series of eight workshops throughout northeastern Colorado during the winters of 1998 and 1999. The purpose of the workshops was to provide beef and dairy producers with the information and tools necessary to develop Comprehensive Nutrient Management Plans (CNMPs). The new EPA/USDA Joint Strategy outlines an expectation that all animal feeding operations (regardless of size) will have CNMPs by
2008. Large livestock producers often hire crop consultants or engineers to develop CNMPs, but the smaller producers can not afford this luxury. Therefore, we aimed these workshops at the smaller producers (<1000 head) and called them, "Do it Yourself Manure Management Workshops."

The "Do it Yourself Manure Management Workshops" were a joint effort between Colorado State University Cooperative Extension and the local Natural Resources Conservation Service. Part of our goal was to illustrate for producers what resources are available in their own counties for support in CNMP development. We provided empty notebooks with dividers in them for each essential part of a CNMP, so that producers could fill their own plans in as they worked through the day and continue the CNMP development in the months thereafter. A workbook is enclosed for your information.

We developed worksheets for producers to fill out for their own operations which they could then insert into the appropriate sections. It was our goal to make this process as simple as possible. The local NRCS offices were especially helpful in providing access to soil surveys and soil map information. Our intention was that producers would work on developing CNMPs specific to their operations during the workshops and would leave knowing what else they needed to do to complete their CNMP.

There were fifty three livestock operations feeding 69,410 head represented at the workshops. In addition, seventeen field staff for NRCS and ten extension agents were also in attendance. Our goal was to help small producers (animal feeding operations with less than 1000 head), and 69% of the producers in attendance did fit this category (Table 1). Although there were substantial numbers of larger cattlefeeders and dairymen, most of them had between 1000 and 2000 head.

Education and Outreach Outcomes

Recommendations for education and outreach:

Areas needing additional study

Future Recommendations

We learned that farmers value manure predominantly for its positive impact on soil physical properties, not for its fertilizer value. This explains why Cooperative Extension's focus on the nitrogen value of manure has not been successful in changing farmer practices. Our new research focus is now on developing BMPs for the utilization of manure to improve soil quality (on eroded soils or otherwise degraded soils, for example). When farmers use manure for high value purposes such as improving soil quality or growing high value crops (such as organic crops), the manure value increases. This allows the economic transport distance to increase, and this will result in reduced concentration of manure in high intensity cattlefeeding areas of the West and protection of water quality in those areas. In other words, using manure to improve soil quality increases manure value and protects water quality, as well.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.